Symmetry Breaking in Interacting Ring-Shaped Superflows of Bose–Einstein Condensates

Abstract

We demonstrate that the evolution of superflows in interacting persistent currents of ultracold gases is strongly affected by symmetry breaking of the quantum vortex dynamics. We study counterpropagating superflows in a system of two parallel rings in regimes of weak (a Josephson junction with tunneling through the barrier) and strong (rings merging across a reduced barrier) interactions. For the weakly interacting toroidal Bose-Einstein condensates, formation of rotational fluxons (Josephson vortices) is associated with spontaneous breaking of the rotational symmetry of the tunneling superflows. The influence of a controllable symmetry breaking on the final state of the merging counter-propagating superflows is investigated in the framework of a weakly dissipative mean-field model. It is demonstrated that the population imbalance between the merging flows and the breaking of the underlying rotational symmetry can drive the double-ring system to final states with different angular momenta.PACS numbers:

Josephson oscillations of chirality and identity in two-dimensional solitons in spin-orbit-coupled condensates

“…Among other applications, the Josephson effect in superconductors may be used for design of qubits [27,28]. Josephson oscillations of angular momentum between annular BECs was investigated too [29][30][31][32][33][34][35][36][37][38]. In these contexts, chirality of the wave functions may play an important role [29], [39][40][41][42][43][44].…”

Persistent current formation in double-ring geometries

“…is the Gross-Pitaevskii operator, and m is the atomic mass of 87 Rb atoms. Here, g 2D = √ 8π 2 a s /ml z is the two-body interaction strength in the two-dimensional (2D) geometry, determined by the s-wave interaction strength a s , µ is the chemical potential, and l z = /mω z is the transverse confinement scale imposed by the harmonicoscillator trap V (z) = mω 2 z z 2 /2.…”

“…The kinetic energy for a winding number n w around a ring of radius R is given by 2 n 2 w /2mR 2 , thus for the parameters we consider here the adopted energy cut-off limits the winding numbers to |n w | 80, far beyond the range we address in this work. Focusing on experimentally relevant geometries for 87 Rb atoms (m = 1.443 × 10 −25 kg and g ≡ mg 2D / 2 = 0.077), we fix the chemical potential µ = 25k B nK and temperature T = 10 nK, chosen to be much lower than the critical temperature of the Berezinskii-Kosterlitz-Thouless (BKT) transition (in the thermodynamic limit) [73],…”

“…In Ref. [79], a ring was populated by two hyperfine states of 87 Rb, and the interference pattern between the rotating and non-rotating states was measured. A commonly employed method is to measure the size of the central hole after a time-offlight expansion, either directly after removal of the trap [33,76], or after transforming the ring trap into a simply connected sheet first, before turning off the trap [76,79].…”

Orbital angular momentum dynamics of Bose-Einstein condensates trapped in two stacked rings

“…Weakly coupled condensates have been proposed as basic building blocks for quantum technologies [38][39][40][41]. In particular, the dynamics of BECs in tunnel-coupled ring potentials have been thoroughly explored in a variety of geometries such as stacked rings with [42,43] or without lattices [44][45][46][47][48], concentric rings [49,50], or coplanar rings [51,52].…”